The current effort for the 3GPP Long Term Evolution (LTE) program is to bring new technology, new architecture, and new methods in the new LTE settings and configurations to provide improved spectral efficiency, reduced latency, and better utilization of the radio resources to bring faster user experiences and richer applications and services with less cost.
As part of these efforts, the 3GPP would like to introduce the concept of a home enhanced Node B (HeNB) in LTE (and also, possibly in a parallel fashion, in Release 8 of WCDMA, GERAN, and other cellular standards). The HeNB refers to a physical device similar to a wireless local area network (WLAN) access point (AP). The HeNB provides users with access to LTE services over extremely small service areas, such as homes or small offices. The HeNB is intended to connect to the operators' core network by using, for example, public Internet connections. This can be particularly useful in areas where LTE has not been deployed and/or legacy 3GPP radio access technology (RAT) coverage already exists. This may also be useful in areas where LTE coverage may be faint or non-existent for radio transmission problems that occur, for example, while in an underground metro or a shopping mall.
The cell (which is the term for the area over which radio coverage provided by the HeNB is available) that is deployed by the HeNB may be accessed only by a group of subscribers who have access to the services of the cell (e.g., a family) and such a cell may be referred to as a HeNB cell, or more commonly, a Closed Subscriber Group (CSG) cell. A HeNB may be used to deploy (usually) one or more CSG cells over the area which LTE coverage is desired. The term CSG cell may be used for a cell deployed by a HeNB for LTE services or by a HNB for WCDMA or other legacy 3GPP RAT services.
Cell selection and reselection criteria for CSG cells are currently an open issue. This raises several other issues:
(1) No priority schemes exist for CSG cells.
(2) The CSG identifier that the WTRU needs to determine whether a CSG cell is configured in its white list is currently in the system information blocks (SIBs). Reading the SIBs for possibly hundreds of CSG cells in a frequency layer might be unnecessarily expensive in terms of time and power consumed.
(3) Other parameters for cell selection and reselection, such as Qhyst and Qoffset, for CSG cells are undefined.